(a) Field of the Invention
This invention relates to power transmission belts and belt drive systems with the same.
(b) Description of the Prior Art
V-ribbed belts are power transmission belts combining the flexibility of flat belts and the high power transmission capacity of V-belts, and are widely used, for example, as automotive accessory drive belts. In a V-ribbed belt of such kind, in order to allow it to withstand a side pressure and enhance the resistance of the back face part to vertical cracking, the back face side of the belt body is covered with a plainly woven reinforced fabric. In the V-ribbed belt, as shown in FIG. 11, the reinforced fabric 30′ is normally disposed at the belt back face so that the directions of warps 31′ and wefts 32′ form equal angles with the widthwise direction of the belt.
In recent years, as belt drive systems for driving automotive accessories, serpentine drive type ones have been increasingly employed which drive a single V-ribbed belt wound about multiple pulleys. In some of such serpentine belt drive systems, in order to accommodate a V-ribbed belt even in their complicated layout, at least one of the multiple pulleys is formed of a flat pulley that makes contact with the belt back face.
When a flat pulley making contact with the belt back face is used, however, there arises a problem that abnormal noises occur between the belt back face and the flat pulley. In the conventional V-ribbed belt, as shown in FIG. 11, the plainly woven reinforced fabric 30′ is disposed at the belt back face so that the directions of warps 31′ and wefts 32′ form equal angles with the belt widthwise direction. As a result, yarn intersections 33′ of the warps and wefts which stand out from the belt surface form lines of bulges 34′ extending in the belt widthwise direction, and the lines of bulges 34′ are arranged at even intervals in the belt lengthwise direction. Therefore, the lines of bulges 34′ each formed by consecutive yarn intersections 33′ in the belt widthwise direction periodically beat the flat pulley to produce abnormal noises.
A technique for solving the above problem is disclosed in Japanese Unexamined Patent Publication No. 2002-235805. In this technique, at least either the wefts or warps of the reinforced fabric are arranged at uneven intervals to locate the yarn intersections of the wefts and warps at uneven intervals in the belt lengthwise direction. Thus, the frequency of vibratile forces of the pulley in contact with the reinforced fabric is dispersed to reduce the peak vibration intensity. Further, in the technique, the angles of arrangement of the wefts and warps of the reinforced fabric with respect to the belt lengthwise direction are made different from each other to reduce the interval of the yarn intersections in the belt lengthwise direction. Thus, the frequency of vibratile forces of the pulley in contact with the reinforced fabric becomes a high frequency departing from the audio frequency range, thereby suppressing noises.